We consider the spatially flat Friedmann-Lemaitre-Robertson-Walker space-time in the teleparallel model of gravity and assume that the Universe is nearly filled by cold dark matter and a nonminimally coupled scalar field with a power-law potential as dark energy. We investigate the possibility that the Universe undergoes a transition from quintessence to phantom phase. An analytical solution for the scalar field is obtained, and necessary conditions required for such a transition are discussed.

Gamma-ray induced air showers are notable for their lack of muons, compared to hadronic showers. Hence, air shower arrays with large underground muon detectors can select a sample greatly enriched in photon showers by rejecting showers containing muons. IceCube is sensitive to muons with energies above $\sim 500\mathrm{GeV}$ at the surface, which provides an efficient veto system for hadronic air showers with energies above 1 PeV. One year of data from the 40-string IceCube configuration was used to perform a search for point sources and a Galactic diffuse signal. No sources were found, resulting in a 90% C.L. upper limit on the ratio of gamma rays to cosmic rays of $1.2\times {10}^{-3}$ for the flux coming from the Galactic plane region ($-80°\lesssim l\lesssim -30°$; $-10°\lesssim b\lesssim 5°$) in the energy range 1.2–6.0 PeV. In the same energy range, point source fluxes with $E^{-2}$ spectra have been excluded at a level of $(E/\mathrm{TeV}{)}^2\mathrm{d}\Phi /\mathrm{d}E\sim {10}^{-12}–{10}^{-11}{\mathrm{cm}}^{-2}{\mathrm{s}}^{-1}{\mathrm{TeV}}^{-1}$ depending on source declination. The complete IceCube detector will have a better sensitivity (due to the larger detector size), improved reconstruction, and vetoing techniques. Preliminary data from the nearly final IceCube detector configuration have been used to estimate the 5-yr sensitivity of the full detector. It is found to be more than an order of magnitude better, allowing the search for PeV extensions of known TeV gamma-ray emitters.

Analysis of experimental data must sometimes deal with abrupt changes in the distribution of measured values. Setting upper limits on signals usually involves a veto procedure that excludes data not described by an assumed statistical model. We show how to implement statistical estimates of physical quantities (such as upper limits) that are valid without assuming a particular family of statistical distributions, while still providing close to optimal values when the data are from an expected distribution (such as Gaussian or exponential). This new technique can compute statistically sound results in the presence of severe non-Gaussian noise, relaxes assumptions on distribution stationarity and is especially useful in automated analysis of large data sets, where computational speed is important.

The Higgs-fermion couplings are sensitive probes of possible new physics behind a stable light Higgs particle. It is then essential to identify the flavor pattern of those interactions. We consider the case in which a strong dynamics lies behind a light Higgs and explore the implications within the minimal flavor violation ansatz. The dominant effects on flavor-changing Higgs-fermion couplings stem in this context from operators with mass dimension $\le 5$, and we analyze all relevant chiral operators up to that order, including loop corrections induced by four-dimensional ones. Bounds on the operator coefficients are derived from a plethora of low-energy flavor transitions, providing a guideline on which flavor-changing Higgs interactions may be open to experimental scrutiny. In particular, the coefficient of a genuinely $CP$-odd operator is only softly constrained and therefore its impact is potentially interesting.

The strongly coupled phase of Yang-Mills plasma with arbitrary gauge group is studied in a $T$ matrix approach. The existence of lowest-lying glueballs, interpreted as bound states of two transverse gluons (quasiparticles in a many-body setup), is analyzed in a nonperturbative scattering formalism with the input of lattice-QCD static potentials. Glueballs are actually found to be bound up to 1.3 $T_c$. Starting from the $T$-matrix, the plasma equation of state is computed by resorting to a formulation of statistical mechanics (Dashen et al.) and favorably compared to quenched lattice data. Special emphasis is put on $\mathrm{SU}(N)$ gauge groups, for which analytical results can be obtained in the large-$N$ limit, and predictions for a $G_2$ gauge group are also given in this work.

The data on $\mathrm{p}\overline{\mathrm{p}}$ elastic scattering at 1.8 and 1.96 TeV are analyzed in terms of real and imaginary amplitudes, in a treatment with high accuracy, covering the whole $t$ range, and satisfying the expectation of dispersion relation for amplitudes and for slopes. A method is introduced for the determination of the total cross section and the other forward scattering parameters and to check compatibility of E-710, CDF, and the recent D0 data. Slopes $B_R$ and $B_I$ of the real and imaginary amplitudes, treated as independent quantities, influence the amplitudes in the whole $t$ range and are important for the determination of the total cross section. The amplitudes are fully constructed, and a prediction is made of a marked dip in $d\sigma /dt$ in the $|t|$ range $3–5{\mathrm{GeV}}^2$ due to the universal contribution of the process of three-gluon exchange.

Theoretical predictions for a $pp\to 2{\rm Y}+X$ cross section at $\sqrt{s}=8\mathrm{TeV}$ for the LHCb and ATLAS kinematical conditions are obtained. A possibility to observe the new hypothetical particles containing two valence $b$ quarks and two valence $\overline{b}$ quarks is discussed.

Measurements of neutral current cross sections for deep inelastic scattering in $e^{+}p$ collisions at HERA with a longitudinally polarized positron beam are presented. The single-differential cross-sections $d\sigma /d{Q}^2$, $d\sigma /dx$ and $d\sigma /dy$ and the reduced cross section $\tilde{\sigma }$ are measured in the kinematic region $Q^2>185{\mathrm{GeV}}^2$ and $y<0.9$, where $Q^2$ is the four-momentum transfer squared, $x$ the Bjorken scaling variable and $y$ the inelasticity of the interaction. The measurements are performed separately for positively and negatively polarized positron beams. The measurements are based on an integrated luminosity of $135.5{\mathrm{pb}}^{-1}$ collected with the ZEUS detector in 2006 and 2007 at a center-of-mass energy of 318 GeV. The structure functions ${\tilde{F}}_3$ and $F_3^{\gamma Z}$ are determined by combining the $e^{+}p$ results presented in this paper with previously published $e^{-}p$ neutral current results. The asymmetry parameter $A^{+}$ is used to demonstrate the parity violation predicted in electroweak interactions. The measurements are well described by the predictions of the Standard Model.

The cross section for $e^{+}{e}^{-}\to \eta J/\psi$ between $\sqrt{s}=3.8\mathrm{GeV}$ and 5.3 GeV is measured via initial state radiation using $980{\mathrm{fb}}^{-1}$ of data on and around the ${\rm Y}(nS)(n=1,2,3,4,5)$ resonances collected with the Belle detector at KEKB. Two resonant structures at the $\psi (4040)$ and $\psi (4160)$ are observed in the $\eta J/\psi$ invariant mass distribution. Fitting the mass spectrum with the coherent sum of two Breit-Wigner functions, one obtains $\mathcal{B}(\psi (4040)\to \eta J/\psi )·{\Gamma }_{e^{+}{e}^{-}}^{\psi (4040)}=(4.8\pm 0.9\pm 1.5)\mathrm{eV}$ and $\mathcal{B}(\psi (4160)\to \eta J/\psi )·{\Gamma }_{e^{+}{e}^{-}}^{\psi (4160)}=(4.0\pm 0.8\pm 1.4)\mathrm{eV}$ for one solution and $\mathcal{B}(\psi (4040)\to \eta J/\psi )·{\Gamma }_{e^{+}{e}^{-}}^{\psi (4040)}=(11.2\pm 1.3\pm 2.1)\mathrm{eV}$ and $\mathcal{B}(\psi (4160)\to \eta J/\psi )·{\Gamma }_{e^{+}{e}^{-}}^{\psi (4160)}=(13.8\pm 1.3\pm 2.1)\mathrm{eV}$ for the other solution, where the first errors are statistical and the second are systematic. This is the first measurement of this hadronic transition mode of these two states, and the partial widths to $\eta J/\psi$ are found to be about 1 MeV. There is no evidence for the $Y(4260)$, $Y(4360)$, $\psi (4415)$, or $Y(4660)$ in the $\eta J/\psi$ final state, and upper limits of their production rates in $e^{+}{e}^{-}$ annihilation are determined.

We study the ($2+1$)-dimensional Dirac equation in a homogeneous magnetic field (relativistic Landau problem) within a minimal length or generalized uncertainty principle scenario. We derive exact solutions for a given explicit representation of the generalized uncertainty principle and provide expressions of the wave functions in the momentum representation. We find that in the minimal length case, the degeneracy of the states is modified, and that there are states that do not exist in the ordinary quantum mechanics limit ($\beta \to 0$). We also discuss the massless case, which may find application in describing the behavior of charged fermions in new materials like graphene.

Short baseline neutrino experiments such as LSND and MiniBooNE seem to suggest the existence of light sterile neutrinos. Meanwhile, current cosmic microwave background and big bang nucleosynthesis measurements place an upper bound on the effective number of light neutrinos, $N_{\mathrm{eff}}$ and the PLANCK satellite will measure $N_{\mathrm{eff}}$ to a much higher accuracy and further constrain the number of sterile neutrinos allowed. We demonstrate that if an MeV dark matter particle couples more strongly to electrons and/or photons than to neutrinos, then $p$-wave annihilation after neutrino decoupling can reduce the value of $N_{\mathrm{eff}}$ inferred from big bang nucleosynthesis and PLANCK. This mechanism can accommodate two eV sterile neutrinos even if PLANCK observes $N_{\mathrm{eff}}$ as low as the standard model theoretical value of 3.046, and a large neutrino asymmetry is not needed to obtain the correct primordial element abundances. The dark matter annihilation also weakens the cosmological upper bounds on the neutrino masses, and we derive a relationship between the change in these bounds and the corresponding change in $N_{\mathrm{eff}}$. Dark matter with an electric dipole moment or anapole moment is a natural candidate that exhibits the desired properties for this mechanism. Coincidentally, a dark matter particle with these properties and lighter than 3 MeV is precisely one that can explain the 511 keV gamma-ray line observed by INTEGRAL. We show that the addition of two eV sterile neutrinos allows this kind of dark matter to be lighter than 3 MeV, which is otherwise ruled out by the cosmic microwave background bound on $N_{\mathrm{eff}}$ if only active neutrinos are considered.

Among the three forms of relativistic Hamiltonian dynamics proposed by Dirac in 1949, the instant form and the front form can be interpolated by introducing an interpolation angle between the ordinary time $t$ and the light-front time $(t+z/c)/\sqrt{2}$. Using this method, we introduce the interpolating scattering amplitude that links the corresponding time-ordered amplitudes between the two forms of dynamics and provide the physical meaning of the kinematic transformations as they allow the invariance of each individual time-ordered amplitude for an arbitrary interpolation angle. In particular, it exhibits that the longitudinal boost is kinematical only in the front form dynamics, or the light-front dynamics (LFD), but not in any other interpolation angle dynamics. It also shows that the disappearance of the connected contributions to the current arising from the vacuum occurs when the interpolation angle is taken to yield the LFD. Since it doesn’t require the infinite momentum frame (IMF) to show this disappearance and the proof is independent of reference frames, it resolves the confusion between the LFD and the IMF. The well-known utility of IMF usually discussed in the instant form dynamics is now also extended to any other interpolation angle dynamics using our interpolating scattering amplitudes.

We study a quantum fermion field on a background nonextremal Kerr black hole. We discuss the definition of the standard black hole quantum states (Boulware, Unruh, and Hartle-Hawking), focussing particularly on the differences between fermionic and bosonic quantum field theory. Since all fermion modes (both particle and antiparticle) have positive norm, there is much greater flexibility in how quantum states are defined compared with the bosonic case. In particular, we are able to define a candidate Boulware-like state, empty at both past and future null infinity, and a candidate Hartle-Hawking-like equilibrium state, representing a thermal bath of fermions surrounding the black hole. Neither of these states have analogues for bosons on a nonextremal Kerr black hole and both have physically attractive regularity properties. We also define a number of other quantum states, numerically compute differences in expectation values of the fermion current and stress-energy tensor between two states, and discuss their physical properties.

We investigate the prospects for constraining alternative theories of gravity with a typical near-term, low-budget 21-cm intensity mapping experiment. We derive the 21-cm brightness temperature perturbation consistently in linear theory, including all line-of-sight and relativistic effects. We uncover new terms that are a small correction on large scales, analogous to those recently found in the context of galaxy surveys. We then perform a Fisher matrix analysis of the $B_0$ parametrization of $f(R)$ gravity, where $B_0$ is proportional to the square of the Compton wavelength of the scalaron. We find that our 21-cm survey, in combination with CMB information from Planck, will be able to place a 95% upper limit of $7\times {10}^{-5}$ on $B_0$ in flat models with a $\Lambda \mathrm{CDM}$ expansion history, improving on current cosmological constraints by several orders of magnitude. We argue that this constraint is limited by our ability to model the mildly nonlinear regime of structure formation in modified gravity. We also perform a model-independent principal component analysis on the free functions introduced into the field equations by modified gravity, $\mu$ and $\Sigma$. We find that 20–30 modes of the free functions will be “well-constrained” by our combination of observables, the lower and upper limits dependent on the criteria used to define the “goodness” of the constraint. These constraints are found to be robust to uncertainties in the time dependence of the bias. Our analysis reveals that our observables are sensitive primarily to temporal variations in $\Sigma$ and scale variations in $\mu$. We argue that the inclusion of 21-cm intensity maps will significantly improve constraints on any cosmological deviations from general relativity in large-scale structure in a very cost-effective manner.

The thermal evolution of strange stars in both normal and color-flavor-locked (CFL) phases are investigated together with the evolutions of the stellar rotation and the $r$-mode instability. The heating effects due to the deconfinement transition of the stellar crust and the dissipation of the $r$-modes are considered. As a result, the cooling of the stars in the normal phase is found to be not very different from the standard one. In contrast, for the stars in the CFL phase, a big bump during the first hundred years and a steep decay ($\sim 7\%$ in ten years) at the ages of $\sim {10}^{4-6}\mathrm{yrs}$ are predicted in their thermal evolution curves. These unique features provide an effective observational test for determining whether or not the CFL phase is reached in strange stars. This thermal test method is independent of and complementary to the rotational test method, which is a direct consequence of the $r$-mode instability [see J. Madsen, Phys. Rev. Lett. 85, 10 (2000)].

We study how generic phase transitions taking place in compact stars constructed in the framework of the Eddington-inspired Born-Infeld (EiBI) gravity can lead to anomalous behavior of these stars. For the case with first-order phase transitions, compact stars in EiBI gravity with a positive coupling parameter $\kappa$ exhibit a finite region with constant pressure, which is absent in general relativity. However, for the case with a negative $\kappa$, an equilibrium stellar configuration cannot be constructed. Hence EiBI gravity seems to impose stricter constraints on the microphysics of stellar matter. Besides, in the presence of spatial discontinuities in the sound speed $c_s$ due to phase transitions, the Ricci scalar is spatially discontinuous and contains $\delta$-function singularities proportional to the jump in $c_s^2$ acquired in the associated phase transition.

We show that for every asymptotically anti–de Sitter (AdS) solution compactified on a torus there is a corresponding Ricci-flat solution obtained by replacing the torus by a sphere, performing a Weyl rescaling of the metric and appropriately analytically continuing the dimension of the torus/sphere (as in generalized dimensional reduction). In particular, it maps Minkowski spacetime to AdS on a torus, the holographic stress energy tensor of AdS to the stress energy tensor due to a brane localized in the interior of spacetime and AdS black branes to (asymptotically flat) Schwarzschild black branes. Applying it to the known solutions describing the hydrodynamic regime in AdS/CFT, we derive the hydrodynamic stress tensor of asymptotically flat black branes to second order, which is constrained by the parent conformal symmetry. We compute the dispersion relation of the Gregory-Laflamme unstable modes through cubic order in the wave number, finding remarkable agreement with numerical data. In the case of no transverse sphere, AdS black branes are mapped to Rindler spacetime and the second-order transport coefficients of the fluid dual to Rindler spacetime are recovered.

We demonstrate that electroweak baryogenesis can occur in a supersymmetric model with an exact $R$-symmetry. The minimal $R$-symmetric supersymmetric model contains chiral superfields in the adjoint representation, giving Dirac gaugino masses, and an additional set of “$R$-partner” Higgs superfields, giving $R$-symmetric $\mu$ terms. New superpotential couplings between the adjoints and the Higgs fields can simultaneously increase the strength of the electroweak phase transition and provide additional tree-level contributions to the lightest Higgs mass. Notably, no light stop is present in this framework, and in fact, we require both stops to be above a few TeV to provide sufficient radiative corrections to the lightest Higgs mass to bring it up to 125 GeV. Large CP-violating phases in the gaugino/Higgsino sector allow us to match the baryon asymmetry of the Universe with no constraints from electric dipole moments owing to $R$ symmetry. We briefly discuss some of the more interesting phenomenology, particularly of the lightest CP-odd scalar.

The radiative decay is believed to be an ideal lab to study the hadronic structure of newly observed resonances because the reactions are governed by only the electromagnetic interaction (tree level). However, to obtain correct theoretical values, one has to properly deal with the nonperturbative QCD effects in the wave function and hadronization. In this work, we derive the formulas for the radiative decays of $0^{++}$ and $1^{-+}$ heavy mesons in the light-front quark model. Because $\mathcal{B}({\chi }_{c0}\to J/\psi \gamma )$ is well-measured, the theoretical evaluation of the transition rate can be used to test our approach. Within this theoretical framework, the width of ${\chi }_{b0}\to {\rm Y}(1S)\gamma$ is evaluated. The formulas can be applied to identify the inner structures of new resonances, for example the isospin of $h_{c(b)}$ and the structure of $D_s(2317)$, via processes $h_c\to {\eta }_c\gamma$, $h_b\to {\eta }_b\gamma$ and $D_s(2317)\to D_s^{*}+\gamma$.

We analyze lattice data for octet baryon masses from the QCDSF Collaboration employing manifestly covariant baryon chiral perturbation theory. It is shown that certain combinations of low-energy constants can be fixed more accurately than before from this data. We also examine the impact of this analysis on the pion-nucleon sigma term and on the convergence properties of baryon mass expansions in the SU(3) symmetry limit.